Bimetallic nanocomposite catalysts fabricated by area ......Bimetallic nanocomposite catalysts...
Transcript of Bimetallic nanocomposite catalysts fabricated by area ......Bimetallic nanocomposite catalysts...
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Bimetallic nanocomposite catalysts fabricated by
area selective atomic layer deposition and applications
Rong Chen, Kun Cao, Yun Lang, Jiaming Cai, Bin Shan
Huazhong University of Science & Technology
2019-04-04
2019 Area Selective Deposition Workshop
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Catalyst for Environment and Energy
Q. Jia et al. ACS catal. 2016
W. Wang et al. Adv. Mater.2017S. Zhang et al. JACS. 2014
S. Cao et al. Catal. Sci. Technol.2017
• Energy and Environment
• Huge demand for noble metals
O2
H2
Fuel cell
PGM market report 2018 Feb Pt, Pd, Ru, Rh, Au, Ag
HC,CH,NOx
CO2,H2ON2
Increasing
2015 2016 2017
Pt Pd Rh Pt Pd Rh Pt Pd Rh
100.5 237.0 23.7 102.2 247.1 25.5 103.6 262.0 26.7
15.5 14.1 2.0 16.1 13.3 2.3 16.1 16.4 2.3
243.9 284.4 28.7 255.6 291.6 31.4 255.6 315.8 32.6
185.8 200.8 23.3 189.2 210.3 23.5 189.9 205.2 23.9
demand
supply
Automobile
Chemical
storage
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Catalyst is designed to be
more active and in lower cost
Core-shell Alloy Monometallic mixture
Catalyst Design is Important
Xie, et al. Nano. Lett. 2014
• Single metal catalyst • Bimetallic catalyst
Alayoglu et al. Nat. Mater. 2008S. Zhang et al. JACS. 2014
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ALD for Constructing Bimetallic Catalyst
• Composition and thickness control by ALD
J.W. Elam et al, Nano Lett. 2010
• ALD technology: conformality, self-limiting surface
W.M.M. Kessels et al. Chem. Mater. 2012
Nanotechnology 2015 4
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5
• Lattice strain
bulkthin
shell
thick
shell
Latt
ice
stra
in
(%)
Alayoglu et al. Nat Mater. 2008
Mikkelsen et al. Chem. Mater.. 2014
Maark et al. J. Phys. Chem.C. 2014
• Ligand effect
MethodsInteraction in Bimetallic Core-shell Catalyst
0 10 20 30 40 50 6070.0
70.2
70.4
70.6
70.8
71.0
71.2
Bin
din
g E
ne
rgy
(eV
)
Au content in PtAu NPs (%)
Pt4f
Interaction between metals
• Chemical state
Nilekar et al. JACS. 2010
ee
• Chemisorption
• The precise structure would lead to better understanding on reaction
mechanism and boost catalytic performance.
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Outlines
• Bimetallic nanoparticles for catalysts
• Catalysts for PROX reaction
Pd@Pt Core-shell nanoparticles
Facet selective Pt on Ru nanoparticles
• Catalyst for DRM reaction
Meshed Co coating on Ni nanoparticles
• Summary
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Pd@Pt : lattice matched, core shell interaction (ligand effect)
Ru@Pt : mismatched crystal constant, lattice strain factor
@Pt
PdRu
@Pt
Lattice strain Ligand effect
PROX: Preferential oxidation of CO
• PROX reaction
• expensive
→ Pt
• high activity
• Catalyst demand
• high selectivity
PROX
1% 10ppm
H2+
CO
H2+
CO2
Catalyst surface
CO CO CO COCO CO
→ M@Pt
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ALD recipe Pd Pt Ru
Precursor
Chamber
temperature200 ºC 300 ºC 275 ºC
Plus/purge
time
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O2
2s 8s 2s 8s
Pd(hfac)2 Formalin
1.6s 8s 2s 8s
MeCpPtMe3 O2
• Growth rate on Si wafer
Nucleation Liner growth
50nm
Pd, Pt and Ru ALD Processes
1.6s 8s 3s 8s
Ru(Etcp)2 O2
O3
0 100 200 300 400
0
3
6
9
12
15
18
Pd Ru
Pt
Film
th
ickn
ess
(n
m)
ALD cycles
50nm
precursors
carrier gasMain chamber
supports
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SAMs Approach for Core-shell Structure
Sci. Rep., 2015, 5, 8470
Strategy for fabricating
core shell NPs
• Utilizing SAMs assisted area selective ALD could refine the nucleation of
shell metal on core and obtain core shell NPs with regular ALD recipes.
pinhole
-CH3 endgroup
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Growth of Pt shell on Pd core
• The size and composition of the core shell NPs can be controlled
precisely by varying the ALD cycles.
Core-shell structure Pt growth process on Pd
QCM
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Activity and Selectivity for PROX Reaction
PROX: CO+H2+1/2 O2 → CO2+H2 CO-tolerant: CO+H2+1/2 O2 → CO+H2O
Preferential oxidation of CO in H2 (PROX) reaction
ChemCatChem, 2016, 8, 326
• The catalyst with 1 ML Pt shell shows optimal catalytic performance and
minimal Pt loading, lowest Ea of it suggesting lower CO oxidation barrier.
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d-band Center Comparison between Ru@Pt & Pd@Pt
• For Pd@Pt catalysts, Pt is coherent on Pd thus the
d band center is influenced solely by ligand effect
Pt(111) on Ru (001)
(1.6% mismatch)
Pt(111) on Pd (111)
Lattice strain & Ligand effect Ligand effect
100
120
140
160
180
200
220
240
260
T50
Ru
Pd
Pt
Pd@Pt
Te
mp
ratu
re /
C
Ru@Pt
• Lower d-band center leads to weaker adsorption
of CO, which would reduce the CO poison effect
• For Pt(111)/Ru (001) surface, the lower d band is
the results of both lattice strain and ligand effect
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Design of Bi-functional Ru-Pt nanoparticles
⚫ The nanoparticles with bi-functional exposed facets shows weaker CO
adsorption (Ru(001)/Pt(111)) and enhanced O2 dissociation(Ru(101)).
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Surface evolution and electron modification effect
• As the Pt coating layer reaches to 5ML, the Pt coating layer becomes
continuous and the surface properties are similar to pure Pt.
• The 1ML Pt-Ru(001) shows lowest T50:As Ru(101) surface is gradually
covered, the activity starts to decrease.
78 76 74 72 70 68
Inte
nsit
y (
a.u
.)
Binding Energy(eV)
(a) (b)Pt 4f 7/2Ru 3p 3/2
70.9
71.1
71.2
Pt4f 5/2
Al 2p 71.3Pure Pt
1MLPt-Ru001
2MLPt-Ru001
5MLPt@Ru
10MLPt@Ru
Pure Pt
461.6462.7
Pure Ru
462.1
Pure Pt
74.4
2200 2150 2100 2050 2000 1950 1900
Wavenumber (cm-1)
A
dso
rban
ce (
a.u
.)468 466 464 462 460 458
Binding Energy (eV)
Inte
nsit
y (
a.u
.)
(c)2090 cm-1
Pt-CO
2030 cm-1
Ru-CO
1MLPt-Ru001
2MLPt-Ru001
5MLPt@Ru
10MLPt@Ru
1MLPt-Ru001
2MLPt-Ru001
5MLPt@Ru
10MLPt@Ru
FTIR reveals the surface evolution
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Outlines
• Bimetallic nanoparticles for catalysts
• Catalysts for PROX reaction
Pd@Pt Core-shell nanoparticles
Facet selective Pt on Ru nanoparticles
• Catalyst for DRM reaction
Meshed Co coating on Ni nanoparticles
• Summary
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Meshed coating of Ni nanoparticles
⚫ Single Co component is less active in DRM reaction, the complete coating
of Co on Ni (Co@Ni core shell structure) will decrease the reactivity
⚫ The meshed coated CoNi catalyst is designed to improve activity and
coking inhibition, the Co component effectively enhance CO2 adsorption
and activation, which helps to remove the carbon species on Ni sites
CO2 Reforming of CH4
Challenge: coking and sintering
Heavy coking
ChemSusChem 2015, 8, 3556; Science 2012, 335, 1205
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Design and Fabrication of meshed coating structure
• First, atomically thin CoOx layers are deposited on Ni with ALD method
• Post reduction of as deposited CoOx layers on Ni, where oxygen release from
CoOx produces a meshed Co coating
J. Catal., 2019 in press17
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Fabrication method for meshed coating structure
• Oxygen is released from CoOx, which
produces a meshed Co coating
CoOx ALD Reduction
Ni Ni@CoOx Ni@Co
Metallic phase
oxidative phase
Meshed Co coating on Ni
• Metallic Co in Ni catalysts could
stabilize the metallic phase of Ni
component, which is beneficial for
activity enhancement
Chemical state of Co
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Catalytic activity and stability
• Excessive amount of Co coating (core shell structure) will cause Ni surface
getting covered, resulting in decrease of activity
• Ni@meshed-Co catalyst has outstanding long-term reaction stability than
the pure Ni-based catalyst
• Co stabilizes the Ni0 content and Co facilitates the adsorption and activation
of CO2, which is beneficial to the activity enhancement
Bare NiCore shell
Meshed coating
Activity Stability
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The Coking Reduction
• The Ni@meshed-Co catalysts surface are mainly non-graphitic carbon species that
can be activated and eliminated
• The higher CO2 conv. produces much less CO, and meshed coating catalysts produces
less CH* intermediates and are fast removed
TG Raman
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Summary
Core shell
structure
Facet selective
coated structure
Meshed like
coated structure
• SAMs assisted selective ALD is applied to fabricate Pd@Pt
core shell nanoparticles, Pt coating layer can be controlled
with atomic monolayer precision showing high activity for
PROX reaction
• Facet selective ALD is achieved through lattice mismatch to
fabricate bi-functional Pt@Ru(001) structure, enhancing the
CO activation and O2 dissociation at the same time for
PROX reaction
• ALD with post reduction treatment is developed to
synthesize meshed Co coating Ni nanoparticles, which is
highly active and coking resistant for DRM reaction